1. Field of the Invention
The present invention relates to a positive photoresist composition that is excellent in sensitivity and definition and is advantageously used for patterning a resist with less shrink.
2. Description of the Related Art
In photolithography processes using i-line (365 nm), demands have been made on photoresist materials that can form an ultrafine resist pattern of not more than half a micrometer, particularly of not more than 0.35 μm. As such photoresist materials, positive photoresist compositions each comprising an alkali-soluble novolak resin and a non-benzophenone naphthoquinonediazido-group-containing compound (a photosensitizer) have been proposed.
For example, Japanese Patent Laid-Open No. 6-167805 mentions that a positive photoresist material using an esterified product between a tetra- to hepta-nuclear linear polyphenol compound and a naphthoquinonediazidosulfonic acid compound is a high-definition material for use in photolithography processes using i-line.
Photolithography processes using short-wavelength light sources such as KrF excimer laser (248 nm) and ArF excimer laser (193 nm) are suitable for the formation of resist patterns of not more than 0.35 μm. However, manufacturing lines using these light sources require a large amount of spending on new plants and equipment, and such spending is nearly unrecoverable.
Under these circumstances, strong demands have been made on the use of the photolithography processes using i-line (365 nm) from now on, which are widely used at present, and techniques of ultrafine processing of resist patterns of not more than 0.35 μm using photoresist materials for i-line irradiation have been examined.
However, it has been believed that by using a light source having a wavelength greater than the size of the resulting resist pattern, a resist pattern having satisfactory sensitivity, definition, focal depth range properties and other properties cannot be obtained. For example, this type of resist patterns exhibits “shrink”, the phenomenon that the resist pattern shrinks in a length direction upon shifting of the focus on the order of submicron from an optimal position during exposure. The shrink is often observed in both edges of a resist pattern comprising regular line-and-space (L&S) traces or in an isolation pattern or irregular resist pattern. Accordingly, the resulting pattern in, for example, a logical IC having complicated traces cannot be obtained in a good yield.